Ohm's law

[leblon]

 I have finally finished writing the book on electricity for kids. Here is a sample chapter about Ohm's law. Don't take the pictures too seriously: they are just placeholders which I made myself. 

Comments

[alexanderr]

I liked it, but I'm not a kid. hard to say if kids would find this interesting or not. If I was writing something like that I would make stronger links to present day. Like the whole "IR drop" thing for example. in microprocessors (say, Intel or AMD, does not matter) voltage supply is very low, like 1V or even less, since higher voltages would simply break the transistors (they are nm-scale and electrical field is very strong). but then there are billions of transistors, so when microprocessor is running the DC current is easily on the scale of 100A (so it dissipates 100W, like a light bulb). now, that puts very severe limits on the R of the on-chip power supply. Like 1 Ohm would not work, and even 0.01 Ohm would still be a very big problem. I mean a simple numerical example like that with pictures of microprocessors might be very entertaining and even enlightening.

another example would be using DC voltage for long-distance power distribution. why using 1 million volt DC is better than lower voltage AC.

since you mention superconductivity I would probably throw in more examples and pictures there. like SMES (superconducting magnetic energy storage) is a very cool application and kids might appreciate that. maybe. or maybe not, I don't know.

[leblon]

DC v AC is discussed in a separate chapter in great detail. Especially because it involves an interesting story ("the war of the currents").

But I did not understand what you are saying about it. Long-distance power distribution systems are all high-voltage AC, aren't they?

[alexanderr]

no, not all

https://en.wikipedia.org/wiki/High-voltage_direct_current

but this is well-known. I mean some of them are still using mercury arc valves, invented in 1902

but honestly I think SMES is way more interesting/fascinating, and it is an actual device that is used in practice (unlike quantum computers). I always thought that running a generator on idle should cover most applications, but turns out there are many places where even the very short drop in power associated with that is not acceptable. and that is where you really need SMES. instant power, and huge, but for a very short period of time, until the generator would come up to full power

[leblon]

Right, I forgot about HVDC.

SMES is very cool indeed, I did not know it is something that it actually used in practice. Where is it used? It seems expensive and power-intensive to have all this cryogenic equipment.

[alexanderr]

there used to be this company (for example), called American Superconductor.
I think they are still around, but I am not sure if they are still working with superconductors.

they used to make and sell actual SMES systems, well, it was in the 1990's. I am not sure if they are still doing that. Here's a typical news story from 1999, regarding SMES shipments by American Superconductor:

https://eepower.com/news/american-superconductor-ships-first-smes-product-to-europe/#

" ...The SMES will be installed in April at Austria Druckguss, an aluminum foundry in Gleisdorf, Austria. The foundry has been experiencing a significant number of plant shut downs owing to momentary sags in electrical voltage caused primarily by lightning storms...."